The present invention relates to wellhead tools and, more particularly, to retrieval tools for back pressure or tree test valves.
A back pressure valve is a check valve installed in a tubing hanger or coupling to retain pressure in a well below a valve. A tree test plug is a check valve installed in a tubing hanger or coupling to retain pressure in a christmas tree above a valve. Typically, a tree test plug is used to seal off pressure adjacent to a blowout preventer and christmas tree mounted on a well so that pressurized fluid can be used to test these devices. Back pressure and tree test plug check valves ordinarily have generally cylindrical bodies with an outside diameter slightly smaller than the bore of the well and are landed on a shoulder in the bore and secured by radially extending members.
Existing retrieval tools comprise generally ring-shaped, unitary bodies having axially extending "fingers" which are fixed to the ring body at the upper end and are freely extending at the lower end. The fingers have spring-like properties and together with the ring body form what is referred to as a "spear". The fingers are provided with members that extend radially outward and are adapted to engage a corresponding retrieval groove on the inner diameter of the check valve to be retrieved. The free ends or other potions of the finger have wedge-shaped outer surfaces below the radially extending members in order to bias the fingers radially inward through camming action during insertion of the spear into the check valve until the extension engages the groove causing the fingers to expand radially outward to lock the spear relative to the valve. Once positioned and locked, the retrieval tool can be used to pull the check valve out of the tubing hanger or coupling.
Such existing retrieval tools are subject to several drawbacks during normal use. Problems arise when, in the case of a christmas tree for instance, a gate valve is inadvertently left partially closed or partially opened restricting the open bore area through which the retrieval tool is supposed to pass. If during insertion one or more fingers get caught on a partially closed gate, or if the fingers are off center, the free end of one or more of the fingers may get caught and be subjected to loads which may damage or deform the fingers. Similar problems can occur when a retrieval tool is run through a blow out preventer stack. Permanent deformation of a finger may prevent the retrieval tool from properly engaging the check valve. Sometimes back pressure valves and tree test plugs get stuck inside the hanger and coupling such that ordinary pulling or retrieval force cannot remove them. In such instances, it is desirable to have a retrieval tool which is capable of releasing from a stuck check valve.